Wheel loader

ABSTRACT

A transmission for a wheel loader includes first and second oil accumulating parts, a communication oil path, a horizontal hole and a vertical hole. The first oil accumulating part accumulates scattered lubricating oil. The second oil accumulating part is mounted to an end of an output shaft below the first oil accumulating part, and accumulates the lubricating oil from the first oil accumulating part. The communication oil path allows the first and second oil accumulating parts to communicate with each other. The horizontal hole extending axially is formed in the rotary shaft, and communicates with the second oil accumulating part. The vertical hole communicating with the horizontal hole is formed in the output shaft, and directs the lubricating oil accumulated in the second oil accumulating part to the lubricated part when the output shaft is rotated at a rotational speed lower than a predetermined rotational speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2012-107451, filed on May 9, 2012, the disclosure of which is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a wheel loader, and particularly to awheel loader executing a work with repetition of travelling andstopping.

BACKGROUND ART

A wheel loader is a vehicle for mainly executing an excavation work andincludes a vehicle body frame, a working unit, front and rear tires, acab and etc. Further, the vehicle body frame includes a front frame, arear frame and a coupling part. The front frame is coupled to the rearframe through the coupling part, while being allowed to turn in theright-and-left direction.

Such wheel loader includes a hydraulic transmission for executingswitching between forward travelling and rearward travelling and gearshifting. Further, the transmission is provided with rotary shafts suchas an input shaft, an intermediate shaft and an output shaft, hydraulicclutch devices attached to these shafts, gears, a parking brake and etc.

Thus, a friction part including a clutch device and a brake device, aslide part such as a bearing, and an engaged part using a spline aredisposed inside the transmission. Therefore, it is required to supplylubricating oil to these components.

In view of this, a hydraulic system as described in Japan Laid-openPatent Application Publication No. JP-A-2010-174971 and a structure asdescribed in Japan Laid-open Patent Application Publication No.JP-A-2001-227563 have been provided.

The hydraulic system described in Japan Laid-open Patent ApplicationPublication No. JP-A-2010-174971 is provided with a transmissionlubricating circuit branched from a high pressure circuit for supplyingan operating oil to a clutch, and is further provided with atransmission lubrication backup circuit branched from a steeringlubricating circuit. The transmission lubrication backup circuit isconnected to the transmission lubricating circuit. Further, the oil usedfor lubrication by these circuits is accumulated in a transmission caseand is then returned to a steering device.

On the other hand, the transmission described in Japan Laid-open PatentApplication Publication No. JP-A-2001-227563 is configured to forciblylubricate the clutch by means of a drain oil of a power steeringmechanism in order to implement clutch lubrication at a low cost.

Further, Japan Laid-open Patent Application Publication No.JP-A-H06-249324 describes arrangement of a tub located above anautomatic gear shifting device as a fueling device of the automatic gearshifting device in order to collect the lubricating oil upwardly stirredby gears within the transmission. The lubricating oil, collected by thetub, is then configured to be supplied to respective slide parts by theaction of gravity.

SUMMARY

In transmissions for wheel loaders, as described in Patent Literatures 1and 2, respective components attached onto the input shaft are oftenlubricated by means of the lubricating oil forcibly supplied thereto bypumps. It could be also assumed that an output part including an outputshaft and etc. is forcibly lubricated similarly to the above. In thiscase, however, it is required to increase the volume of an oil pump forsupplying lubricating oil and cost is increased by providing anadditional circuit.

In view of the above, natural lubrication is often executed for a splineengaged part such as an output shaft disposed on the bottom part of atransmission case by upwardly stirring and scattering lubricating oilaccumulated on the bottom part of the case through gear rotation andetc.

Now, wheel loaders often execute works at a low speed. Especially insuch situation that a work is executed at a low speed for a long periodof time, sufficient lubricating oil is not easily supplied to respectivecomponents by means of conventional natural lubrication. Especially, aparking brake of a wheel loader is attached to an end portion of a caseof a transmission. Therefore, a brake plate and a spline engaged part,which form a parking brake device, cannot be sufficiently lubricated bymeans of the conventional natural lubrication.

It is required to raise the oil surface level of the lubricating oilwithin the case to the height of the spline engaged part in order towell lubricate the spline engaged part and etc. by means of theconventional natural lubrication. In such structure, however, stirringresistance by a rotary member is increased in the lubricating oil andpower loss is increased.

It is an object of the present invention to achieve sufficient supply ofthe lubricating oil to respective components by means of naturallubrication in a transmission for a wheel loader.

A V-shape work is known as a representative work to be executed by awheel loader of the present invention. The V-shape work is a type ofwork described as follows.

In short, an excavation work is executed in a given position, andsubsequently, a load such as earth and sand, put in a bucket, is liftedup by elevating a boom while the vehicle is moved rearwards.Subsequently, the transmission is switched from rearward travelling toforward travelling, and the boom is further lifted up while the vehicleis moved forwards for approaching a dump truck. Then, the bucket isdumped for discharging the earth and sand onto the dump truck.Subsequently, the vehicle is moved back and forth without being loadedand is again returned to the excavation position.

As described above, during execution of the V-shape work, the vehiclespeed is alternately transitioned back and forth across a given vehiclespeed (hereinafter referred to as “a boundary vehicle speed”) between avehicle speed less than the boundary vehicle speed and a vehicle speedgreater than or equal to the boundary vehicle speed.

In view of the above, through the utilization of a characteristic workof a wheel loader, the present invention is configured to execute suchlubrication that is natural lubrication but is similar to forcedlubrication.

In short, a wheel loader according to a first aspect of the presentinvention includes an engine, a working unit and a transmissionexecuting switching between forward travelling and rearward travellingand gear shifting. The working unit is configured to be driven by meansof a pressurized oil to be produced by driving of the engine. Thetransmission includes a case and a rotary shaft disposed inside the caseand a lubricated part disposed on an outer peripheral part of the rotaryshaft. The transmission includes a first oil accumulating part, a secondoil accumulating part, a communication oil path, a horizontal hole and alubrication oil path. The first oil accumulating part is disposed abovethe lubricated part and accumulates a scattered lubricating oil. Thesecond oil accumulating part is mounted to an end of the rotary shaftwhile being disposed below the first oil accumulating part, andaccumulates the lubricating oil from the first oil accumulating part.The communication oil path makes the first oil accumulating part and thesecond oil accumulating part communicate with each other. The horizontalhole is formed in the rotary shaft while being axially extended, andcommunicates with the second oil accumulating part. The lubrication oilpath has a vertical hole that is formed in the rotary shaft while beingradially extended from an outer peripheral surface of the rotary shaft,and communicates with the horizontal hole. Further, the lubrication oilpath is configured to direct the lubricating oil accumulated in thesecond oil accumulating part to the lubricated part when the rotaryshaft is rotated at a rotational speed lower than a predeterminedrotational speed.

The term “predetermined rotational speed” herein refers to a rotationalspeed determined by the relation in magnitude between the potentialenergy of the first oil accumulating part with respect to the second oilaccumulating part and the kinetic energy of the lubricating oil withinthe second oil accumulating part (which is generated by centrifugalforce) due to rotation of the output shaft. Specifically, when thekinetic energy is greater than the potential energy, the lubricating oilwithin the second oil accumulating part is pressed onto acircumferential wall portion of the second oil accumulating part and isaccordingly pushed back within the communication oil path without beingsupplied into the horizontal hole. As described above, the thresholdrotational speed at which the kinetic energy becomes greater than thepotential energy is “predetermined rotational speed”.

In the present wheel loader, the lubricating oil scattered within thecase of the transmission is accumulated in the first oil accumulatingpart in such situation as when the vehicle is travelling. Then, duringexecution of a V-shape work of the wheel loader, when the vehicle speedis less than a predetermined vehicle speed, i.e., when the rotationalspeed of the rotary shaft is less than a predetermined rotational speed,the lubricating oil accumulated in the first oil accumulating part isdirected to the second oil lubricating part disposed below the first oilaccumulating part by means of the action of gravity, and is furthersupplied to the lubricated part through the lubrication oil path havingthe horizontal hole and the vertical hole.

Despite natural lubrication, the lubricating oil is herein forciblysupplied to the lubricated part by utilizing the potential energy of thelubricating oil accumulated in the first oil accumulating part at a lowspeed during execution of a V-shape work of the wheel loader. Therefore,the lubricating oil can be supplied to a position to which thelubricating oil cannot be easily supplied by means of naturallubrication.

A wheel loader according to a second aspect of the present inventionrelates to the wheel loader of the first aspect, and wherein the rotaryshaft is an output shaft disposed on a bottom part of the case and thefirst oil accumulating part has a predetermined length along an axialdirection of the output shaft. Further, the communication oil path isformed in the case.

Here, the lubricating oil accumulated in the first oil accumulating partis directed to the second oil accumulating part through thecommunication oil path formed in the case. In this case, it is notrequired to externally dispose a pipe for making the both oilaccumulating parts communicate with each other.

A wheel loader according to a third aspect of the present inventionrelates to the wheel loader of the second aspect, and wherein thetransmission further includes an output flange spline-engaged with anend of the output shaft. Further, the second oil accumulating part is anshaft end space produced between an end surface of the end of the outputshaft and a cap that is fixed to the output flange while being disposedaxially away from the end surface of the output shaft at a predeterminedclearance. The horizontal hole is formed in a center part of the outputshaft.

Here, the second oil accumulating part is formed by utilizing the spaceexisting on the shaft end portion of the output shaft. Therefore, aspecial space is not required.

A wheel loader according to a fourth aspect of the present inventionrelates to the wheel loader of the third aspect, and wherein thetransmission further includes a parking brake that is attached to alateral part of the case while being spline-engaged with the outputshaft. Further, the vertical hole makes the horizontal hole and a splineengaged part of the parking brake communicate with each other.

In many cases, no input-side mechanism and/or member is disposed abovethe parking brake that is attached to the lateral part of the case whilebeing spline-engaged with the outputs shaft. Therefore, it is difficultto supply the lubricating oil to the parking brake by means of naturallubrication.

In view of the above, according to the wheel loader of the fourthaspect, the lubricating oil is configured to be supplied to thespline-engaged part of the parking brake through the vertical hole.

A wheel loader of a fifth aspect of the present invention relates to thewheel loader of any of the first to fourth aspects, and wherein thefirst oil accumulating part is integrally formed with an inner wall ofthe case and forms a U-shaped cross section together with the innerwall.

Here, the first oil accumulating part is formed by utilizing the innerwall of the case. Therefore, the first oil accumulating part can beformed with a simple structure.

A wheel loader according to a sixth aspect relates to the wheel loaderof any of the second to fifth aspects, and wherein the transmissionfurther includes an input mechanism that has a rotary shaft and a gearabove the output shaft and is supplied with the lubricating oil.Further, the first oil accumulating part accumulates a scattered oilfrom the input mechanism and a scattered oil upwardly stirred from thecase bottom part.

In general, the input mechanism is often forcibly lubricated. Further,the lubricating oil used for lubrication of the input mechanism drops onthe case bottom part or is scattered by the rotary member.

In view of the above, the lubricating oil in the aforementionedsituations is configured to be accumulated in the first oil accumulatingpart. Therefore, the lubricating oil can be efficiently accumulated inthe first oil lubricating part, and as a result, the output shaft partcan be well lubricated.

A lubrication method of a transmission for a wheel loader according tothe present invention is a method of lubricating the wheel loadertransmission including a first oil accumulating part, a second oilaccumulating part and a lubricated part. The first oil accumulating partis mounted on an inner wall of a case of the transmission. The secondoil accumulating part is mounted on an end of a rotary shaft disposedbelow the first oil accumulating part while communicating with the firstoil accumulating part through a communication path. The lubricated partis disposed on an outer peripheral part of the rotary shaft. Further,the lubrication method includes the following steps.

A step of accumulating a scattered lubricating oil in the first oilaccumulating part.

A step of directing the lubricating oil to the lubricated part throughthe second oil accumulating part by means of a potential energy of thelubricating oil accumulated in the first oil accumulating part when therotary shaft is rotated at a rotational speed lower than a predeterminedrotational speed.

It should be noted that the term “predetermined rotational speed” in thelubrication method is similar to the aforementioned rotational speed.

ADVANTAGEOUS EFFECTS OF INVENTION

As described above, according to the present invention, lubricating oilcan be sufficiently supplied to respective components in a transmissionfor a wheel loader by means of natural lubrication utilizing gravity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a wheel loader according to an exemplaryembodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a transmission.

FIG. 3 is a cross-sectional view of a lubrication mechanism of thetransmission.

FIG. 4 is an external perspective view of a front case and a rear case.

FIG. 5 is a diagram representing transition of the vehicle speed of thewheel loader during execution of a V-shape work.

FIG. 6 is a diagram representing a relation between vehicle speed andlubricating oil supply.

DESCRIPTION OF THE EMBODIMENTS Overall Structure of Wheel Loader

FIG. 1 illustrates an entire structure of a wheel loader 1 according toan exemplary embodiment of the present invention. It should be notedthat FIG. 1 is a side view of the wheel loader 1.

The wheel loader 1 includes a vehicle body frame 2, a working unit 3, apair of front tires 4, a cab 5, an engine compartment 6 and a pair ofrear tires 7.

The vehicle body frame 2 has so-called an articulated structure andincludes a front frame 11, a rear frame 12 and a coupling part 13. Thefront frame 11 is disposed forwards of the rear frame 12 and is coupledto the rear frame 12 through the coupling part 13 while being allowed toturn in the right-and-left direction. A drive train, including anengine, a transmission and etc., is installed in the rear frame 12.

The working unit 3 includes a lift arm 15 and a bucket 16. The lift arm15 and the bucket 16 are driven by means of pressurized oil to besupplied thereto from a hydraulic pump (not illustrated in the figures).The base end of the lift arm 15 is rotatably supported by the frontframe 11. The bucket 16 is rotatably attached to the distal end portionof the lift arm 15.

The cab 5 is mounted on the rear frame 12, and a handle for a steeringoperation, a joystick, an operating member for operating the workingunit, a variety of display devices and etc. are disposed inside the cab5.

Transmission Overall Structure

The transmission installed in the present wheel loader serves totransmit torque, which is inputted thereto from two hydraulic motors, toan output shaft. Specifically, the transmission includes first andsecond hydraulic motors. The first hydraulic motor is coupled to a firstinput shaft through a clutch mechanism, while the second hydraulic motoris directly coupled to a second input shaft. Further, the first inputshaft is provided with a planetary gear mechanism having a largereduction ratio.

Further, when a large torque is required in executing a work and etc.,the clutch mechanism is turned on and torque is inputted into thetransmission from the first and second hydraulic motors through theinput shafts to which the first and second hydraulic motors arerespectively coupled. On the other hand, in such a case of high speedtravelling, the clutch mechanism mounted on the first input shaft isturned off and torque is inputted into the transmission only from thesecond hydraulic motor for high speed travelling through the secondinput shaft.

The entire structure of the transmission will be hereinafter explainedusing FIG. 2. As illustrated in FIG. 2, a transmission 20 includes afront case 21, a rear case 22, an input part 23 accommodated in thecases 21 and 22, an output part 24 and a parking brake 25 attached tothe rear part of the rear case 22.

Input Part

As described above, the input part 23 includes two hydraulic motors andtwo gear shifting mechanisms. Each of the two gear shift mechanismsincludes an input shaft and a gear mechanism for gear shifting andtransmits torque from its corresponding hydraulic motor to the outputshaft. FIG. 2 partially illustrates one of the two gear shiftingmechanisms. The gear shifting mechanism illustrated in FIG. 2 includes afirst input shaft 31, the clutch mechanism (not illustrated in thefigures), a planetary gear mechanism (only partially illustrated) and aninput gear 35.

The first input shaft 31 is coupled to the output shaft of the firsthydraulic motor (not illustrated in the figures) through a splineengagement. Further, the torque inputted into the first input shaft 31is inputted into a ring gear 32 of the planetary gear mechanism throughthe clutch mechanism (not illustrated in the figures). A plurality ofplanet gears 33 are meshed with the ring gear 32, while being rotatablysupported by a carrier 34. The input gear 35 is fixed to the carrier 34.The input gear 35 is rotatably supported through a bearing by an endcover 36 fixed to the rear case 22.

Output Part

The output part 24 includes an output shaft 41 and an output gear 42.

The output shaft 41 is disposed on the bottom parts of the cases 21 and22. One end of the output shaft 41 is rotatably supported by the frontcase 21 through a bearing, while an axially intermediate part thereof isrotatably supported by the rear case 22 through a bearing. A firstspline 41 a for flange engagement is formed on the outer peripheralsurface of the one end of the output shaft 41. Similarly, a secondspline 41 b for flange engagement is formed on the outer peripheralsurface of the other end of the output shaft 41. The second spline 41 bhas an axial length greater than that of the first spline 41 a. Further,a third spline 41 c for gear engagement is formed on the axiallyintermediate part of the output shaft 41.

A first output flange 43 is spline-engaged with the first spline 41 a ofthe output shaft 41, while a second output flange 44 is spline-engagedwith the second spline 41 b. The first output flange 43 is fixed to oneend surface of the output shaft 41 by means of a plate 45 and a bolt 46.Further, a cap 47 is fitted into an opening of the second output flange44, while a predetermined clearance G1 is produced between the cap 47and the other end surface 41 d of the output shaft 41.

The output gear 42 is spline-engaged with the third spline 41 c. Theinput gear 35 illustrated in FIG. 2 and another input gear (notillustrated in the figures) are meshed with the output gear 42. Itshould be noted that a baffle plate 48 is disposed for enclosing thesurrounding of the lower part of the output gear 42.

Parking Brake

The parking brake 25 is attached to a lateral surface of the rear case22 on the second output flange 44 side. The parking brake 25 includes ahousing 51, a cover 52, a hub 53, a stationary ring 54, a plurality ofbrake plates 55, a piston 56 and a plurality of disc springs 57.

The housing 51 is formed in a roughly ring shape and is fixed to alateral surface of the rear case 22 together with the cover 52 by meansof a plurality of bolts 60. The cover 52 is fixed to an end surface ofthe housing 51. A dust seal 61 and an oil seal 62 are mounted betweenthe inner peripheral part of the cover 52 and the outer peripheralsurface of the second output flange 44. It should be noted that the dustseal 61 and the oil seal 62 are similarly disposed on the first outputflange 43 side.

The hub 53, the stationary ring 54, the plural brake plates 55, thepiston 56 and the plural disc springs 57 are accommodated in the spaceformed by the housing 51 and the cover 52 as described above.

The hub 53 is formed in a ring shape and a spline formed on the innerperipheral surface thereof is spline-engaged with the second spline 41 bof the output shaft 41. Further, the hub 53 has a plurality of teeth onthe outer peripheral surface thereof.

The stationary ring 54 is fixed to a lateral surface of the rear case 22by means of a bolt 64 while being disposed on the outer peripheral sideof the hub 53. The stationary ring 54 has a plurality of teeth on theinner peripheral surface thereof.

The plural brake plates 55 include a first plate to be engaged with thehub 53 and a second plate to be engaged with the stationary ring 54. Inother words, the first plate has a plurality of teeth on the innerperipheral part thereof, and the teeth are meshed with the teeth formedon the outer peripheral surface of the hub 53. Further, the second platehas a plurality of teeth formed on the outer peripheral part thereof,and the teeth are meshed with the teeth formed on the inner peripheralsurface of the stationary ring 54. Friction members are disposed on theboth lateral surfaces of the first plate.

The piston 56 is formed in a ring-like and tube-like shape and isdisposed movably in the axial direction along the inner peripheralsurface of the housing 51. An oil chamber 65, supplied with theoperating oil for actuating the piston 56, is formed between the outerperipheral surface of the piston 56 and the inner peripheral surface ofthe housing 51.

The plural disc springs 57 are disposed in the inner periphery of thepiston 56 while being disposed between the piston 56 and the cover 52.The plural disc springs 57 are set in a compressed state. Therefore,while the operating oil is not being supplied to the oil chamber 65, thepiston 56 causes the plural first and second plates to be pressedagainst each other by the plural disc springs 57.

In the parking brake 25 structured as described above, braking is turnedon and rotation of the output shaft 41 is braked, while oil chamber 65is not supplied with the operating oil. On the other hand, the piston 56is moved to a side away from the plural brake plates 55 when the oilchamber 65 is supplied with the operating oil. Therefore, the first andsecond plates, forming the brake plates 55, are released from pressingagainst each other and braking is turned off. In the state, braking withrespect to the output shaft 41 is released.

Lubrication Mechanism

FIG. 3 illustrates a part extracted from the lubrication mechanismmounted to the transmission 20. In the present exemplary embodiment, theinput part 23 is forcibly lubricated by means of the lubricating oil tobe supplied from an oil pump. On the other hand, the output part 24 islubricated by means of the lubricating oil fallen or scattered from theinput part 23 and the lubricating oil scattered by the output gear 42and etc. The lubrication structure will be hereinafter specificallyexplained.

As illustrated in FIG. 2, a first hole 71 for supplying lubricating oilis axially formed in the end cover 36. The first hole 71 is communicatedwith a second hole 72 formed coaxially with the center axis of the firstinput shaft 31. The lubricating oil, supplied from the oil pump (notillustrated in the figures) through these holes 71 and 72, is suppliedto the bearings and slide portions through clearances formed amongrespective components and holes formed in the radial direction. Further,the first input shaft 31 also has a third hole 73 axially formed in thecenter part thereof, and the lubricating oil is supplied to the clutchmechanism and etc. mounted to the first input shaft 31 through the thirdhole 73 and the radially formed holes (not illustrated in the figures).

As illustrated in FIG. 3, a first oil accumulating part P1, a second oilaccumulating part P2, a horizontal hole 84, and oil paths OP1 and OP2for lubrication are provided for lubricating the output part 24.

The first oil accumulating part P1 is a part for mainly accumulating thelubricating oil supplied to and scattered from the input part 23. Asillustrated in FIGS. 3 and 4, the first oil accumulating part P1 isintegrally formed with the inner wall of the front case 21 and that ofthe rear case 22 and forms a U-shaped cross section together with theinner walls. When explained in more detail, a part of a bottom portionP1 a, a part of a lateral portion P1 b and a front wall P if of thefirst oil accumulating part P1 are formed in the front case 21. Further,a large part of the bottom portion P1 a, a large part of the lateralportion P1 b and a rear wall P1 r of the first oil accumulating part P1are formed in the rear case 22. Then, in matching the front case 21 andthe rear case 22 to each other at mating surfaces 21 a and 22 a, thefirst oil accumulating part P1 having a U-shaped cross section is formedby the bottom portion P1 a, the lateral portion P1 b, the case innerwall surface and the front and rear walls P1 f and p1 r. It should benoted that a fourth hole 74 is formed in the lower part of the rear wallP1 r while axially penetrating therethrough.

As described above, the second oil accumulating part P2 is the clearanceG1 produced between the cap 47 attached to the second output flange 44and the end surface 41 d of the output shaft 41.

The horizontal hole 84 is formed along the axial direction in the centerpart of the output shaft 41 and has a predetermined depth from one endsurface 41 d of the output shaft 41. In other words, one end of thehorizontal hole 84 is opened to the clearance G1.

The oil paths for lubrication include: the communication oil path OP1for directing the lubricating oil accumulated in the first oilaccumulating part P1 to the second oil accumulating part P2; and thesupply oil path OP2 for directing the lubricating oil accumulated in thesecond oil accumulating part P2 to respective components.

The communication oil path OP1 includes the aforementioned fourth hole74 and fifth to ninth holes 75 to 79. The fifth hole 75 is formed in thehousing 51 of the parking brake 25 while being axially penetratingtherethrough, and is communicated with the fourth hole 74. The sixthhole 76 is formed in the cover 52 of the parking brake 25 along theaxial direction while being communicated with the fifth hole 75. Thesixth hole 76 is formed at a predetermined depth from the mating surfaceof the housing 51. The seventh hole 77 is formed in the cover 52 alongthe radial direction, while having a predetermined depth from the outerperipheral surface of the cover 52 to the inner peripheral side. Thesixth hole 76 is communicated with an intermediate part of the seventhhole 77. The eighth hole 78 is axially formed at a predetermined depthfrom the cover 52 surface supporting the disc springs 57, while beingcommunicated with the seventh hole 77. The ninth hole 79 is communicatedwith the eighth hole 78 and the inner peripheral part of the cover 52.

A predetermined space G2 is produced in a part to which the ninth hole79 is opened. Specifically, the space G2 having an annular shape isformed by the outer peripheral surface of the output shaft 41, the tipend surface of the second output flange 44 and a seal member 80 disposedon the inner peripheral part of the cover 52. The ninth hole 79 iscommunicated with the space G2.

It should be noted that a snap ring 81 is mounted to an end surface ofthe seal member 80 for inhibiting the lubricating oil accumulated in thespace G2 from leaking towards the seal member 80 through the secondspline 41 b of the output shaft 41.

Further, the spline inner teeth of the second output flange 44 ispartially removed, and a toothless portion is thus formed therein. Theclearance G1 and the space G2 are communicated mainly through aclearance produced by the toothless portion and the output shaft 41.

The supply oil path OP2 includes first and second vertical holes 85 aand 85 b. The first vertical hole 85 a is radially formed in the axiallyintermediate part of the output shaft 41. At an end portion of theoutput gear 42, the first vertical hole 85 a makes the outer peripheralsurface of an end portion of the third spline 41 c of the output shaft41 and the horizontal hole 84 communicate with each other. The secondvertical hole 85 b is radially formed while being disposed laterally tothe first vertical hole 85 a. At the inner peripheral surface of the hub53, the second vertical hole 85 b makes the outer peripheral surface ofan end portion of the second spline 41 b of the output shaft 41 and thehorizontal hole 84 communicate with each other.

Lubrication of Output Part

Particularly, a lubrication action of the output part 24 will be hereinexplained where a V-shape work is being executed.

The V-shape work is as described above, and FIG. 5 represents transitionin the vehicle speed during execution of a V-shape work. In this examplerepresented in FIG. 5, one cycle of works (1) to (4) is executed roughlyin 30 seconds. Specifically, in Step (1), the vehicle is forwardly movedwithout being loaded and executes an excavation work. In Step (2), thevehicle is backwardly moved while lifting up a load such as earth andsand within the bucket. In Step (3), the vehicle is forwardly movedwhile holding the load, then approaches a dump truck and discharges theearth and sand onto the dump truck. In Step (4), the vehicle isbackwardly moved without being loaded, changes a travel directionthereof and is returned to the excavation position again.

As represented in FIG. 5, during execution of a V-shape work asdescribed above, the vehicle speed is alternately transitioned back andforth across a boundary vehicle speed between a low speed lower than theboundary vehicle speed and a vehicle speed higher than or equal to theboundary vehicle speed. The boundary vehicle speed is a vehicle speed atwhich a balance is produced between the centrifugal force (kineticenergy) generated in the lubricating oil accumulated in the second oilaccumulating part P2 by means of rotation of the output shaft 41 and thepotential energy of the lubricating oil accumulated in the first oilaccumulating part P1. Respective components are herein supposed to belubricated in shaded regions in FIG. 5, i.e., in periods of time whenthe vehicle travels at a vehicle speed lower than the boundary vehiclespeed. Therefore, lubrication is supposed to be effective for roughlyhalf of the time during execution of a V-shape work of 30 seconds percycle.

The boundary vehicle speed will be explained in more detail. Thelubricating oil accumulated in the first oil accumulating part P1 isdirected to the second oil accumulating part P2 through the respectiveholes 74 to 79, the clearance G2 and the second spline 41 b. Then,respective components are lubricated by the lubricating oil accumulatedin the second oil accumulating part P2 through the horizontal hole 84and the two vertical holes 85 a and 85 b. In this case, the pressure ofmaking the lubricating oil flow towards the respective components is thepotential energy of the lubricating oil accumulated in the first oilaccumulating part P1 (hereinafter referred to as “a supply head of thelubricating oil”).

On the other hand, when the output shaft 41 is rotated, centrifugalforce acts on the lubricating oil accumulated in the second oilaccumulating part P2. When the rotational speed of the output shaft 41then becomes greater than or equal to a predetermined rotational speed,the centrifugal force acting on the lubricating oil in the second oilaccumulating part P2 (hereinafter referred to as “centrifugal hydraulicpressure”) becomes greater than the supply head of the lubricating oil.Accordingly, the lubricating oil is moved to the outer peripheral partin the clearance G1 of the second oil accumulating part P2, and thereby,the lubricating oil no longer exists in the center part of the clearanceG1 and the horizontal hole 84.

The boundary vehicle speed is the vehicle speed where the supply head ofthe lubricating oil and the centrifugal hydraulic pressure of thelubricating oil in the second oil accumulating part P2 (the clearanceG1) are equal to each other (the rotational speed of the output shaft41) under such condition as described above.

FIG. 6 represents a relation between the vehicle speed and thelubricating oil supply. In FIG. 6, OH indicates the supply head of thelubricating oil, i.e., the pressure of making the lubricating oil flowinto the horizontal hole 84 of the output shaft 41. Further, CPindicates the centrifugal hydraulic pressure attributed to travelling(rotation), i.e., the pressure of obstructing the flow of thelubricating oil into the horizontal hole 84.

As is obvious from FIG. 6, in the vehicle speed range lower than theboundary vehicle speed (a left side in FIG. 6), the supply head OH ofthe lubricating oil is greater than the centrifugal hydraulic pressureCP and respective components are lubricated. Specifically, thelubricating oil accumulated in the first oil accumulating part P1 isdirected to the clearance G2 through the fourth to ninth holes 74 to 79.Further, the lubricating oil is directed from the clearance G2 to theclearance G1 of the second oil accumulating part P2 through the secondspline 41 b. The lubricating oil in the clearance G1 then flows throughthe horizontal hole 84 by means of the supply head, and is furthersupplied to the spline engaged part, the slide part and further a groupof the plural brake plates 55 of the parking brake 25 through the firstand second vertical holes 85 a and 85 b.

On the other hand, when the vehicle speed becomes greater than or equalto the boundary vehicle speed (a right side in FIG. 6), the centrifugalhydraulic pressure CP becomes greater than the supply head OH of thelubricating oil. The lubricating oil in the clearance G1 is herein movedto the outer peripheral part, and thereby, the lubricating oil no longerexists in the center part of the clearance G1 and the horizontal hole84. Therefore, respective components are not lubricated in the vehiclespeed range.

It should be noted that in the vehicle speed range greater than or equalto the boundary vehicle speed, the lubricating oil is scattered torespective components by rotary members such as gears. Further, thelubricating oil, forcibly supplied to the input part 23, is alsoscattered within the cases 21 and 22. Thus scattered lubricating oil isaccumulated in the first oil accumulating part P1. The lubricating oil,accumulated in the first oil accumulating part P1 in the vehicle speedrange greater than or equal to the boundary vehicle speed, is used forlubricating the respective components of the output part 24 in the lowspeed range lower than the boundary vehicle speed.

In the shaded time ranges of FIG. 5, the respective components of theoutput part 24 are lubricated by the lubricating oil accumulated in thefirst and second oil accumulating parts P1 and P2.

Features

(1) The respective components of the output part 24 and the parkingbrake 25 are lubricated by utilizing a characteristic work form of awheel loader. Therefore, the lubricating oil can be sufficientlysupplied to positions not easily supplied with the lubricating oil bymeans of natural lubrication.

(2) The first oil accumulating part P1 is formed with use of the innerwalls of the cases 21 and 22. Therefore, the first oil accumulating partP1 can be formed with a simple structure.

(3) The first oil accumulating part P1 and the second oil accumulatingpart P2 are communicated through the oil paths formed in the rear case22, the housing 51 of the parking brake 25 and etc. Therefore, a pipingis not required for making the both oil accumulating parts communicatewith each other.

(4) The second oil accumulating part P2 is formed by utilizing theclearance G1 residing at the shaft end of the output shaft 41.Therefore, a special space is not required.

Other Exemplary Embodiments

The present invention is not limited to the exemplary embodiment asdescribed above, and a variety of changes or modifications can be hereinmade without departing from the scope of the present invention.

(a) In the aforementioned exemplary embodiment, the output part of thetransmission is configured to be lubricated. However, a similarlubrication structure can be also applied to the other mechanismsincluding the intermediate shaft and etc.

(b) The structures of the first and second oil accumulating parts P1 andP2 are not limited to those of the aforementioned exemplary embodiment.The oil accumulating parts may be formed by utilizing other spaces,recesses and etc.

(c) The lubricating oil paths are not limited to the vertical holes 85 aand 85 b in the aforementioned exemplary embodiment. The lubricating oilpaths may be clearances and etc. formed among the respective members.

In the transmission for a wheel loader of the illustrated embodiments,lubricating oil can be sufficiently supplied to respective components bymeans of natural lubrication utilizing gravity.

1. A wheel loader comprising: an engine; a working unit configured to bedriven by a pressurized oil produced by driving of the engine; atransmission including a case, an output shaft disposed on a bottom partof the case, and a lubricated part disposed on an outer peripheral partof the output shaft, the transmission being configured and arranged toexecute switching between forward travelling and rearward travelling,and gear shifting, the transmission further including a first oilaccumulating part disposed above the lubricated part and having apredetermined length along an axial direction of the output shaft, thefirst oil accumulating part accumulating a scattered lubricating oil, anoutput flange spline-engaged with an end of the output shaft, a secondoil accumulating part disposed below the first oil accumulating part andformed by an shaft end space formed between an end surface of the end ofthe output shaft and a cap, the cap being fixed to the output flange anddisposed axially away from the end surface of the output shaft at apredetermined clearance, the second oil accumulating part accumulatingthe lubricating oil from the first oil accumulating part, acommunication oil path formed in the case and allowing the first oilaccumulating part and the second oil accumulating part to communicatewith each other, a horizontal hole formed in a center part of the outputshaft and extending axially, the horizontal hole communicating with thesecond oil accumulating part, and a lubrication oil path having avertical hole, the vertical hole being formed in the output shaft andextending radially from an outer peripheral surface of the output shaft,the lubricating oil path communicating with the horizontal hole, thelubrication oil path being configured to direct the lubricating oilaccumulated in the second oil accumulating part to the lubricated partwhen the output shaft is rotated at a rotational speed lower than apredetermined rotational speed.
 2. (canceled)
 3. (canceled)
 4. The wheelloader recited in claim 1, wherein the transmission further includes aparking brake attached to a lateral part of the case, the parking brakespline-engaged with the output shaft, and the vertical hole allows thehorizontal hole and a spline engaged part of the parking brake tocommunicate with each other.
 5. The wheel loader recited in claim 1wherein the first oil accumulating part is integrally formed with aninner wall of the case and forms a U-shaped cross section together withthe inner wall.
 6. The wheel loader recited in claim 1 wherein thetransmission further includes an input mechanism, the input mechanismhaving a rotary shaft and a gear above the output shaft, the inputmechanism supplied with the lubricating oil, and the first oilaccumulating part accumulates a scattered oil from the input mechanismand a scattered oil upwardly stirred from the case bottom part. 7.(canceled)